The invention relates generally to a process of removing impurities from hydrocarbon or petroleum products, and more particularly, to a process of removing impurities from hydrocarbon fuels which includes the removal and prevention of microbial contamination.
Petroleum products may be purified by treatment with an oxidizing agent, such as sulfuric acid. In such a process, oxidation of impurities generally causes formation of an insoluble sludge, as well as soluble acid products which may be absorbed onto an absorbent material such as an activated clay. The use of hydrogen peroxide in addition to or as a substitute for the mineral acids in the oxidation process has also been suggested.
In addition to the naturally occurring impurities found in crude oil derivatives, which may be removed by oxidation of the oil, another impurity which has caused serious problems for the petroleum industry has been the presence and growth of microbial contamination. Such microbial activity has caused especially serious problems in jet aircraft fuel systems. The microbiological contamination of jet fuel can result in the plugging of filters which, when coupled with the high rate of fuel consumption of jet aircraft, may quickly cause malfunctioning of the fuel control system. Large amounts of sludge which causes such malfunctioning often results from the presence of bacteria and their matabolic by-products.
Microbial contamination is most pronounced in hydrocarbons such as jet fuels. Jet fuels, such as JP4, JP5 and JP6 generally contain a large percentage of kerosene or kerosene-type hydrocarbons. Such hydrocarbons, which are made up of paraffins with minor amounts of aromatics, are easily attached by microorganisms. Also, such fuels may contain minor amounts of olefins, sulfur, oxygen and nitrogen compounds, which for many microorganisms are essential for growth. Thus, the presence of these and other compounds in addition to the hydrocarbons when left in the fuel will result in more rapid microbial contamination.
One essential ingredient for the presence and growth of microorganisms is moisture. Kerosene or larger hydrocarbon-chain type fuels, being denser and more viscous than gasoline, have a greater tendency to entrain free water and hold it in suspension. Also, these fuels more readily form stable water emulsions. A wide range of microorganisms may exist in a hydrocarbon fuel in the presence of water. Several organisms can exist in a hydrocarbon environment with very little or perhaps no water, but in turn may produce additional water and by-products which allow the growth of an even more varied group of organisms. Thus, it can be seen that a hydrocarbon fuel, unless maintained in a completely anhydrous state, may, upon extended storage, be contaminated with a large amount of biological sludge.
The presence of microbial contamination may not only cause malfunctioning of the fuel system, but also has been attributed to fuel tank corrosion, since microorganisms may release corrosive by-products. Particularly serious corrosion problems have been encountered in integral fuel tank systems found in many jet aircraft. In such systems, the fuel is stored in the fuselage or wing section and is in direct contact with the aircraft metal. In addition, such integral fuel tank systems are often sealed with an elastomeric material such as acrylonitrilebutadiene (Buna-N) or polysulfides. These sealants themselves may provide the required nutrients for the growth of many microorganisms, as for example, sulfur organisms in polysulfide sealed tanks.
Although microbial contamination has caused the most serious problems in jet fuels and jet fuel systems and thus has been most extensively studied in this connection, it should be recognized that microbial contamination also occurs in other hydrocarbon and petroleum products such as gasolines and oils.
The microorganisms which may form in a hydrocarbon environment can include bacteria, fungi, protista yeast and mold. The bacteria which may be present may include heterotrophic bacteria, autotrophic bacteria, sheathed and stalked bacteria, and sulfur bacteria.
Heterotrophic bacteria are those microorganisms which require an organic carbon source and are unable to use carbon dioxide as the only source of carbon. A large number of heterotrophic bacteria have been found in fuel sludges, and they may include
Baccillus megatherium sp. PA1 Staphylococcus epidermitis and var. PA1 Pseudomonas sp. PA1 Serratia sp. PA1 Flavobacterium sp. PA1 Bacillus myocides PA1 Bacillus subtilis PA1 Aerobacter aerogenes PA1 Clestridium sp. PA1 Coccus sp. PA1 Pseudomonas fluorescens PA1 Escherichia sp. PA1 Desulfovibrio sp. PA1 Iron bacteria PA1 Thiobacillus sp. PA1 Fusarium moniliforme PA1 Cladosporium (fungi species) PA1 Flavobacterium arborescens PA1 Clostridium sporogenes PA1 Desulfovibrio desulfuricans PA1 Aerobacter aerogenes PA1 Bacillus subtilis PA1 Pseudomonas aeruginosa PA1 Pseudomonas fluorescens PA1 Cladosporium resinae PA1 Aeremonium PA1 Fusarium PA1 Alternaria PA1 Bacillus terminalis PA1 Flavobacterium fulvum PA1 Bacillus megaterium PA1 Flavobacterium diffusum PA1 Achromobacter PA1 Pseudomonas oleovorans PA1 Pseudomonas (all species) formicans PA1 Salmonella schottmuelleri PA1 Salmonella typhimurium PA1 Salmonella oranienburg PA1 Salmonella typhosa PA1 Klebsiella pneumoniac PA1 Achromobacter sp PA1 Aerobacter aerogenes PA1 Aerobacter cloacae PA1 Diplococcus pneumoniae PA1 Escherichia coli PA1 Escherichia freundii PA1 Escherichia intermedium PA1 Micrococcus citreus PA1 Micrococcus pyogenes var. albus PA1 Micrococcus pyogenes var. aureus PA1 Paracolobactrum intermediates PA1 Proteus mirabilis PA1 Proteus morganii PA1 Proteus sp PA1 Proteus vulgaris PA1 Sarcina sp PA1 Shigella madampenis PA1 Streptococcus pyogenes, alpha hemolytic PA1 Streptococcus pyogenes, beta hemolytic PA1 Yeast in addition to the fungi and bacteria listed above
Autotrophic bacteria are microorganisms that can obtain energy from carbon dioxide alone in the presence of light, with such species as Desulfovibrio, iron bacteria, and Thiobacillus being found in fuel sludges.
The sheathed bacteria are bacterial cells surrounded by a sheath composed of an organic substance which may be impregnated with iron or manganese hydroxide. Of this class, galliomella species, caulobacter species, and sederocapsa species have been found in fuels. T. thiooxidans, T. thioparus, and T. dentrificans are examples of sulfur bacteria which may be found in fuel contamination.
As previously discussed, metallic corrosion may be caused by microorganisms. It has been demonstrated that such bacteria as
are involved in metallic corrosion. Corrosion, as well as much of the sludge formation, may result from the by-products of such microorgams. For example, a large variety of digestion related materials may be produced from such organisms, including enzymes, proteins, and fatty acids. These, in turn, may break down into simpler oxygen, nitrogen, sulfur, and carbon compounds. For example, oxygen containing by-products may include organic acids, alcohols, aldehydes, or ketones. Nitrogen containing by-products may include ammonia, amines, imides, amides, nitrates, and nitrites. The sulfur containing by-products from such microorganisms may include mercaptans, sulfides, disulfides, thioacids, dithioacids, thioaldehydes, and thiones as well as sulfur from the sulfur bacteria itself. The formation of such by-products results in extensive corrosion of a fuel tank.
Particular microorganisms, which are known to be associated with fuel and cutting oils, include
To date, the problem associated with microbial contamination caused by these organisms has been dealt with by attempting to minimize the amount of moisture condensing into the fuel, as well as limiting the amount of time that the fuel is stored, or utilizing high cost maintenance and housekeeping procedures, e.g., filtration, skimming, etc., or a wide array of additives to inhibit or slow the growth of such contamination or to counter the effects thereof. Treatment of fuels has in large been limited to the use of inhibitors, separation of natural impurities and by-products of microbial contamination, as opposed to the elimination and prevention of growth of the organisms themselves or their regrowth.
A major advantage of the process of this invention is that it provides a means of removing not only natural crude oil impurities and the by-products of microbiocidal growth, but also eliminates fuel-born microorganisms and prevents further growth and regrowth of the same.
An additional advantage of the present invention is that natural impurities generally separated during the oil refining process may be separated in a single process along with the microbial contaminants before, during or after the refining process for crude, distilled or otherwise fractionated petroleum products.